Bed covers, particularly blankets, duvets and quilts are used to provide comfort, protection, and/or warmth. Typically, such articles create a zone between the body and the surrounding air which impedes an exchange of heat between the body and the surroundings and thereby reduce the radiation and dissipation of heat from the human body.
Depending on certain factors such as, for example, the ambient temperature, it may be desired that more or less of the heat produced by the human body escape through a bed cover.
If the ambient temperature is low and the heat gradient is thus relatively high then the bed cover might preferably retain more of the heat produced by the body. If, on the other hand, the ambient temperature is relatively high then it may be desired that more heat be carried away from the body.
It is known to use different bed covers in the summer compared to those used in the winter. Bed covers for the winter, for example, are designed in such a way that they retain or maintain (sometimes referred to as “thermal maintenance”) the heat of the human body to a higher extent than bed covers for the summer. Bed covers for the winter generally are thicker and or have a more dense filling material than bed covers for the summer.
In the summer, a winter bed cover could be too warm and provide more thermal maintenance than is required or desired. Body heat builds up under the bed cover since the heat produced by the body is not carried away due to the low heat conductivity and the relatively low temperature drop from under the bed cover to the ambient environment. Bed covers for the summer are therefore generally lighter and less dense that bed covers for the winter. They also generally have a higher number of thermal bridges that permit the body heat to pass through the bed cover and dissipate. They therefore generally provide a lower degree of thermal maintenance compared to a winter bed cover.
In certain circumstances it may be desired to provide a single bed cover with warmer and cooler zones. For example, if one bed partner prefers to be warmer while the other prefers to be cooler it would be advantageous to provide a bed cover which can accommodate both partners.
It is known to use a summer bed cover for the summer months and a winter bed cover when it gets colder. In these circumstances, the bed cover not being used must be stored which is inconvenient and uses up storage space. It is also more expensive and consumes more resources to obtain two bed covers rather than just one.
It is also known to use a bed cover system where several individual bed covers can be combined into one overall bed cover which is thicker for the winter. For example, duvets are available with specific insulation values. Lower values being suitable for summer use and higher values for winter use, each duvet having only one insulation value and the user combines the two duvets by laying one over the other. This arrangement is inconvenient and the winter bed cover is heavier and less comfortable to sleep under.
It is also known to use an adjustable bed cover that involves adjustable straps or cords to adjust the alignment of insulating units in the bed cover to modify the overall thermal insulation of the bed cover. Also known is a reversible bed cover that has a flat sheet with heat insulating panels protruding off from the flat sheet, wherein the thermal insulation of the bed cover can be altered by turning the bed cover over so that the insulating panels face downwards towards the human body. See for example, WO 92/18036, U.S. Pat. No. 5,044,032 and WO 2005/016082 A1.